Digital cameras are known in the prior art and in their simplest form comprise a light, typically a flash light, a sensor containing image sensitive nodes and image storage nodes, a lens or series of lenses and a memory bank. The digital camera is known to be employed as an image capture device for capturing images of documents, and in operation is held in a fixed position over a document. The flash light is then triggered thus illuminating the document. The lens serves to focus the image onto the light sensitive nodes and the image is transferred to light storage nodes within the sensor. The final image is read out to a suitable memory bank where it is stored indefinitely awaiting a final process, for example, downloading onto a computer hard-drive or floppy disk.
However, a digital camera employed in this manner as a document image capture device has severe limitations due to the phenomena of specular reflections. Typically, most documents consist of a glossy material, which reflects light to a large extent. When the flashlight of the digital camera is triggered, high energy specular reflected light is incident on the light sensitive nodes of the sensor resulting, ultimately, in a glare spot within the final image, this glare spot effectively masking certain features of the document.
The problem of glare spots has been recognised in a different field (medical imaging—imaging of the cervix for detection of cervical cancer). U.S. Pat. No. 6,088,612 proposes a solution in which two light sources are used, and the glare-affected parts of an image taken with one light source are replaced by the glare-free parts of the image taken with the other light source. However, obtaining two complete document images containing the two glare spots, requires the camera to receive, process and store twice as much information as would be required if only one image was obtained. This process for irradiating glare spots in this manner is therefore a relatively expensive process in terms of data storage capacity and processing time.